1. Field of the Invention
This invention concerns means for electronically measuring the synchronization of a combustion engine.
2. Description of the Prior Art
It is known from U.S. Pat. No. 3,823,606, to determine the compression pressure in the cylinders of a combustion engine by measuring the starter current when turning the engine over with suppressed ignition. The starter's current consumption maxima during the compression strokes of the individual cylinders of the engine are measured in this method. The starter current is determined in this method by means of the voltage drop at the grouding strap. In order to be able to compare the compression pressures of different vehicles, the grounding straps must be standardized regarding their resistance. The type of starter motor of course also influences its current comsumption. The signal obtained in this prior art manner is an analog signal which must first be converted into a digital signal before it can be processed further in a so called computer diagnosis. It is for these reasons that there is need for a method by which to compare compression pressures independent of the current consumption of the starter motor. The method should furnish a digital value as directly as possible.
It is known that, when turning a combustion engine over by means of a starter motor and at suppressed ignition, there occur synchronization fluctuations of the engine which result from surmounting the compression pressures during the compression strokes of the individual pistons in the cylinders. What is meant by synchronization fluctuations is that the starter motor and thus the crank shaft, cam shaft and distributor coupled thereto will not rotate at a constant speed but will tend to slow down in speed as compression increases. Normally, the higher the compression is the more effect this will have on the slowing down of rotational speed. Possible differences in these synchronization fluctuations give an indication of different compression pressure in the individual cylinders. These differences are particularly apparent in a crank angle range near the top dead center of each piston during its compression stroke.
It is an object of the invention to provide a circuit, by means of which the synchronization fluctuations can be measured.